No. 7.] CARl'KNTER — ]>KEP-SKA LIFE. 423 



tiipply of oxygen which lias most influence on Animal Life ia 

 the deep seas. This is regulated by the general flow of water 

 near the sea- bottom, — a flow not confined to any particular pass- 

 age or area, but maintained by diff'ereucc of specific gravity, 

 produced by diff'erence of temperature. As sea-water, in this 

 respect difi:oriug from fresh-water, continues to increase in density 

 down to its freezing-point, which is 27^ F. if agitated, and 25® 

 F. if still, the Polar column will outweigh the Equatorial column, 

 and there will be a lateral outflow at the bottom towards the 

 -equatorial area. This will cause a lowering of water in the 

 polar area, and produce a surface-flow of water from the Equa- 

 tor towards the Poles. The two bottom-flows from either pole 

 will thus meet near the Equator, and rising, will bring cold 

 water nearer to the surface there than anywhere else, except 

 where the surface itself is subjected to cold. In this way the 

 bottom-temperature of the South Atlantic would be lower than 

 that of the North Atlantic, by reason of the less restricted body 

 of the polar flow in the former. The tables given in the "Chal- 

 lenger's " report confirm the conclusions thus arrived at. From 

 these we find that the general temperature of the North Atlantic 

 bottom is about 35J^ or 36° F., decreasing to 34° F. near St. 

 Thomas, and under the Equator itself to 324° F., the lowest 

 temperature of all. This section proves that the South Atlantic 

 under-flow extends north of the Equator, as had been previously 

 surmised by the lecturer. Only one section was made in the 

 South Atlantic, and no temperatures lower than 33J° F. were 

 there obtained, the expedition not happening to hit upon the 

 channel which brought in the water at 32-4° F. found under the 

 Equator. Most remaikable of all is the line of 35° F. which 

 can be traced across the South Atlantic and then gradually 

 slopes down in the North Atlantic till it is lost. The tempera- 

 ture of the North Atlantic depths is probably about 3° F. higher 

 than in the South Atlantic. Off" the coast of Lisbon, in lat. 38° 

 N., the line of 40° F. is found at 700 to 800 fathoms; in lat. 

 22° N. at 700 fathoms; and on the Equator at 300 fathoms 

 only, descending from a surface temperature of 75° F. The 

 reason for this has been already shown to be the continual rise 

 of the Polar under-flow towards the surface in the Equatorial 

 belt. A further confirmation of these views is obtained from a 

 comparison of specific gravities. The density (due to salinity) 

 of surface-water increases from the poles to the tropics, while 



